Cogito
Grade 4 Math · Chapter 7 · Lesson 3
Angles Add Together
Two turns side by side make one bigger turn.
10 problems · about 15 minutes · 4.MD.C.7
What this lesson teaches
The child adds and subtracts angle measures for adjacent angles.
- Angles sharing an arm add together.
- A missing part is found by subtracting.
- Turning twice is one longer turn.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Naming and Measuring Angles: Is 75 degrees acute or obtuse?
Answer Acute.
Why 75 degrees is acute.
Review — An Angle Is a Turn: How many degrees is a half turn?
Answer 180
Why 180 degrees, a straight line.
Warm Up
Straightforward practice. Get the method working first.
4 problemsA right angle split into 25 and one more part. How big is that part?
Answer 65
Why 65 degrees.
What happens to angle measures when two angles sit side by side?
Answer They add.
Why Angle measure is additive.
35 degrees plus 55 degrees?
Answer 90
Why That makes a right angle.
A right angle split into 20 and one more part. How big is that part?
Answer 70
Why 90 − 20.
Build It Up
The same ideas with more to keep track of.
2 problemsA straight angle split into 65 and one more part. How big is that part?
Answer 115
Why 180 − 65.
90 degrees plus 90 degrees?
Answer 180
Why Two right angles.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsTwo Turns: A 40 degree turn and then a 25 degree turn. How many degrees in all?
Answer 65 degrees
Why 65 degrees.
The Missing Part: A straight angle is split into 110 degrees and one more part. How big is that part?
Answer 70 degrees
Why 70 degrees.